The Maunu family's pool didn't seem far from their Los Angeles home until they needed something. Then it felt like a few hundred miles away. "We like to barbecue down there, and we were forever having to run back for ketchup, mustard, or napkins," says Peter Maunu. "It got old."

Maunu's attention turned to a small former horse shed near the pool, which until then had seemed best suited for storage. The family decided to make it their poolhouse and guest suite. It was not an overnight transformation. "At first, I did a lot of the work myself," says Maunu. After installing a new concrete floor and covering the rough interior walls with gypsum board, he created cabinets and a built-in bed, making the space comfortable enough for changing clothes or sleeping.

Michael Blatt, an architect and family friend, helped take the project to the next level. His task was to add a bathroom and a dining area. But when running in a sewer line turned out to be cost-prohibitive, Blatt found inspiration in a surprising spot ― a state-park bathroom. "I knew that [the poolhouse] would be a somewhat primitive structure," he says. "I thought of how bathrooms in parks are indoor/outdoor spaces. We decided to make this a similar space, with everything exposed and a slightly midcentury modern feeling that relates to the main house."

The result is a bathroom that's both elegant and rustic. To solve the plumbing problem, Blatt installed an Incinolet (www.incinolet.com or 800/527-5551), an electric toilet that incinerates rather than flushes waste. A corrugated roof pays homage to the original shed and park shelters. Exposed plumbing for the sink and shower is offset by the cantilevered glass wall with its exposed struts. "We made it from panes I salvaged from an aircraft factory," Blatt says.

To connect the building to the pool and provide a shelter for meals, the architect designed a shade trellis. "Before, it got brutally hot," Maunu says. "Now we use the area a lot for dining or hanging out." Because of Maunu's experimental approach- which seemed appropriate for such an informal structure ― he and the architect were able to solve some unique design dilemmas. "Consider all the options," Maunu says. "We did things here we didn't do in the regular house ― and we're really happy with the results."